Conventional antenna devices include a ⅝-λ monopole antenna device (λ represents a radio wavelength), a single-spiral antenna device, and patch antenna device.
Incidentally, not all of the above antennas are publicly known. The term “spiral” here means not only helical shapes, but also arc shapes.
However, the conventional antenna devices described above do not provide any sufficient performance in terms of directivity, efficiency, or the like.